#include  <stdio.h>
#include  <math.h>
double  fun(double x[ ], int n)
{	int i;
    double avg=0.0, sum=0.0;
	for (i=0; i<n; i++) 
		avg += x[i];
	avg /= n;
	for (i=0; i<n; i++) 
		sum += (x[i]-avg)* (x[i]-avg);
	return sqrt(sum/n);
}
main( )
{  double score[12] ={50,60,70,80,90,100,55,65,75,85,95,99};
   double aa;
   aa= fun(score,12);
   printf("%f\n", aa);
}